IDLs

Odessa innovation week. Developers day
Interface Definition Languages
Ruslan Shevchenko
<ruslan@shevchenko.kiev.ua>
@rssh1
Consultant @ Lynx Capital Partners

Plan
❖ Historical Overview [1990-2015]
❖ from Sun RPC and CGI to Thrift & RESTFull services
❖ Today-s landscape
❖ IDL-s and today application patterns
❖ Future

Historical Overvies: early times
1990. Web not exists yet.
Xamarin modes is discussed:
• two-sided hyperlinks
• decentralized document servers
• publishing hyperlink = publishing document
Protocols: File exchange.
Terminal Access
Custom
Services on top of command-line
or custom protocols

Historical Overview: ONC RPC
1991 - 1995 Sun (then ONC) RPC
RPC = Remote Procedure Call Service specs = C structures
+ function deﬁnitions
Some RPC-based services are still in use
(NFS)
RPC still available in standard Unix-based
OS distributives. (Linux/MacOS/FreeBSD)

Historical Overview: ONC RPC (2)
Service specs = C structures
+ function deﬁnitions
struct request {
int from;
int to;
};
struct result {
int number;
string line<>;
struct result *next;
};
typedef result *res_list;
program DEMO_SERVER {
version DEMO_VERSION {
res_list get_line(request) = 1;
} = 1;
} = 0x20000023;
generate code
Server stub
Client stub

Historical Overview: CGI
1993 CGI (NASA http server, than W3C)
CGI = Common Gateway Interface
No service specs.
Inputs of programs are request
Name/Value pairs (as strings)
Standard output of external program
directed to browser

Historical Overview: CGI (2)
local ($buffer, @pairs, $pair, $name, $value, %FORM);
# Read in text
# Split information into name/value pairs
@pairs = split(/&/, $buffer);
foreach $pair (@pairs)
{
($name, $value) = split(/=/, $pair);
$value =~ tr/+/ /;
$value =~ s/%(..)/pack("C", hex($1))/eg;
$FORM{$name} = $value;
}
$ﬁrst_name = $FORM{ﬁrst_name};
$last_name = $FORM{last_name};
print "Content-type:text/htmlrnrn";
print "<html>";
print "<head>";
print "<title>Hello - Second CGI Program</title>";
print "</head>";
print "<body>";
print “&function()“;
print "</body>";
print "</html>";
1;

Typed/Untyped interfaces
❖ Typed = IDL-based.
❖ RPC
❖ CORBA IDL
❖ SOAP
❖ Zeroc
❖ Thrift
❖ Google protobuf, gRPC
❖ Cap ’n proto
❖ Message Pack
❖ ……………..
❖ Untyped …
❖ CGI, Fact-CGI, …
❖ Plain XML
❖ Json, Jsonp
❖ RESTfull
❖ Auro
❖ Hessian
❖ Bjson
❖ BERT, BERT-RPC
❖ ………..
Dichotomy up to today

Historical Overview: CORBA
1991-1993. CORBA-1.0-1.2
• more general architecture guidelines then concrete standard.
• mapping to C
1996. CORBA-2.0
• IIOP (Interoperability)
• IDL mapping to C++ and Smalltalk,
1999 - 2001. Gold Times. CORBA-2.1 - 2.6
• Over 700 participants in OMG.
• W3C want to adopt CORBA as next web API (instead CGI)
• Portable Naming/Event/Service, Realtime specs, Valuetypes
• Ofﬁcial mapping to 14 programming languages (unofﬁcial to alll)
2002. CORBA-3.0

1991-1993. CORBA-1.0-1.2
• mapping to C
1996. CORBA-2.0
• IIOP (Interoperability)
• IDL mapping to C++ and Smalltalk,
1999 - 2001. Gold Times. CORBA-2.1 - 2.6
• Over 700 participants in OMG.
• W3C want to adopt CORBA as next web API (instead CGI)
• Portable Naming/Event/Service, Realtime specs, Valuetypes
• Ofﬁcial mapping to 14 programming languages (unofﬁcial to all)
2002. CORBA-3.0
Nobody cares, Industry have switched to XML

Reasons to migrate away from CORBA to XML-based RPC:
❖ CORBA Complexity and learning curve.
❖ // XML is easy - just print
❖ XML can be read by human.
❖ Easy usage from script languages
❖ XML is HTTP-based / Not need to open ﬁrewalls for new ports
❖ First CORBA systems was too ﬁne-grained and slow.
❖ // When you print XML, you native design is coarse-grained

Historical Overview: XML-RPC/SOAP
1998. XML-RPC, (Microsoft)
2000. SOAP-1.1 = Simple Object Access Protocol.
• W3C recommendation
• RPC still guidelines. WSDL-1.0
2002 - 2005. Gold Times. SOAP-1.2 +
• WSDL-1.1 is formalization of WSDL-1.0
• OASIS: more than 100 XMLbased vertical standards.
• UDDI: universal registry of web applications.
• First public draft of WSDL-1.2
2007. WSDL-2.0 (=WSDL-1.2) become W3C standard

1998. XML-RPC, (Microsoft)
2000. SOAP-1.1 = Simple Object Access Protocol.
• W3C recommendation
• RPC still guidelines. WSDL-1.0
2002 - 2005. Gold Times. SOAP-1.2 +
• WSDL-1.1 is formalization of WSDL-1.0
• OASIS: more than 100 XMLbased vertical standards.
• UDDI: universal registry of web applications.
• First public draft of WSDL-1.2
2007. WSDL-2.0 (=WSDL-1.2) become W3C standard
Nobody cares, Industry have switched to JSON/REST

Reasons to migrate away from XML-based RPC to JSON:
❖ WSDL/SOAP Complexity and learning curve.
❖ // JSON is easy - just print
❖ JSON can be read by human.
❖ Easy usage from script languages.
❖ XML is too bloated.

Historical Overview: JSON-based API-s
2001. JSON (Douglas Crockford)
• Used for interaction for client-side javascript
2000. REST = Representational State Transfer.
• Phd of Roy Thomas.
• Architecture guidelines without concrete speciﬁcation.
• Formulated in terms of XML API.
2002. Yahoo implements 1-st public JSON-based web service
2006 - 201(>5). Gold times.
• RESTfull/JSON is ‘default’ API for web apps
• Validation: JSONPath, JSONScheme, JSONRPC
• Typed extensions [Auro], binary variants [BJSON].
?

Mainstream loop
❖ Adoption <~~> Complexity
❖ Sometimes we need to do really complex things.
❖ Advanced technology become complex
❖ New loop with ‘something simple’.

IDL-based architecture today
Actually useful
❖ google protocol buffers, grpc: google.
https://developers.google.com/protocol-buffers/
❖ thrift: facebook. (opened via submiting to Apache)
https://thrift.apache.org/
❖ cap-n-proto: Sandstorm.ua
https://capnproto.org/
❖ Other …
❖ zeroc (http://zeroc.com)
❖ MessagePack (http://msgpack.org)
❖ FlatBuffers, SOE (Simple Object Encoding)
❖ …………………………
Pretty close to main ideas of CORBA IDL,
Still have no valuetypes

Good as
❖ Hight-level micro service description.
❖ Javadoc-like tools (if you steel use Json/REST: look at swagger)
❖ Static veriﬁcation of interfaces.
Pay attention too:
❖ Async calls .
❖ Message passing interfaces (local API ).
❖ Traceability. (req-id)

IDL & microservices.
❖ UI boundaries != IDL boundaries.
❖ Discovery (Naming)/ health monitoring
❖ UI = service with interface for:
❖ event generation. (req)
❖ event consumption
❖ Design for failure failure analysis
❖ Structured logging

Future directions
Learning curve ~ task complexity
software development ~ car driving
Gradual complexity

Thanks for attention.
❖ Questions, discussions:
❖ @rssh1
❖ ruslan@shevchenko.kiev.ua
❖ https://github.com/rssh

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